(1) Field of the Invention
The invention relates to a transmission apparatus, and more particularly to a transmission apparatus including a gear and a rack which the gear and the rack can mesh smoothly without accidental tooth collision.
(2) Description of the Prior Art
In the industry, transmission apparatus is widely used in every field for power transmission, alternation of power motion, speed reduction and so on. Common components seen in a typical transmission apparatus are gears, racks, transmission shafts, chains, etc.
Referring to FIG. 1, a conventional transmission apparatus is shown to have a spur gear 1 and a mating rack 2. The spur gear 1 as the driving end of the transmission apparatus is fixed on a driving shaft 3 connecting a motor (not shown here). As shown, the spur gear 1 is rotated clockwise (direction B) to have the respective mating rack 2 move along a linear direction A. During continuous meshing between gear teeth 11 of the spur gear 1 and rack teeth 21 of the rack 2, the rotation of the spur gear 1 can drive the rack 2 to move linearly along the direction A. As shown in FIGS. 2, 3, and 4, a typical teeth mesh between the gear teeth 11 and the rack teeth 21 is demonstrated continuously. For example, when the rack 2 is moved by an exterior force, the rack 2 is pushed toward the gear 1 as shown in FIG. 2 to mesh the gear tooth 11 and the rack tooth 21. Then as shown in the FIG. 3, the gear tooth 11 engages the rack tooth 21 and the gear 1 start to drive the rack 2 as shown in FIG. 4.
Referring to FIG. 5, it is quite often that the mesh between the gear tooth 11 and the rack tooth 21 is initiated by a hitting, or say gear interference, of the gear tooth 11 onto the rack tooth 21, i.e. an accidental collision in between. In particular, such an accidental collision may interrupt the transmission between the spur gear 1 and the rack 2.
To improve the accidental collision between teeth 11, 21, a leading rack tooth 22 with a cutout portion is introduced to initiate the mesh between the spur gear 1 and the rack 2. Upon such an arrangement, the initial teeth hitting between the spur gear 1 and the rack 2 can be lessened.
Though the improvement as shown in FIG. 6 can somehow resolve the initial teeth hitting problem, yet the leading rack tooth 22 is weak in strength and thus may shorten the service lifetime of the rack 2 as well as the transmission apparatus.